(A) study on performance and stability of polysilicon thin-film transistors using ECR plasma thermal oxide as gate insulator

Abstract

High quality active polysilicon film and clean oxide/poly-Si interface are the key factors for realizing high-performance low-temperature poly-Si TFT``s. Although the characteristics of poly-Si film have been improved satisfactorily, and certainly well established, it is not easy to find a low-temperature gate dielectric film which has good bulk and interface properties. The electron cyclotron resonance (ECR) plasma thermal oxidation method has been investigated to grow a high quality oxide film at low-temperature. We have systematically investigated the properties of ECR plasma thermal oxide and the effects of ECR plasma thermal oxidation on the performance and stability of poly-Si TFT``s. The growth characteristics of ECR plasma thermal oxide was investigated varying several process parameters such as substrate temperature, microwave power, and process pressure. It was found that the growth rate of ECR plasma oxide is proportionally dependent on the oxygen plasma density. The plasma density increases with increasing microwave power while it decreases with increasing O2 flow rate within the process pressure ranges from 1mTorr to 4mTorr. The physical constants determined by using Deal-Grove model were significantly high compared with the thermal oxidation. The linear and parabolic rate constants of the ECR plasma oxide grown at 400 C were found to be -0.14 um/h and $9.8\times10^-4 um^2/h$, respectively. The physical, chemical, and electrical characteristics of the oxide grown on crystalline-Si wafer were generally comparable to those of thermal oxide. The oxide exhibited a breakdown field over 8 MV/cm, a fixed oxide charge density (Nff) of $7\times10^10 cm^-2$, and a interface state density (Nit) of $4\times10^10 cm^-2eV^-1$. The ECR plasma thermal oxide has been investigated as the gate insulator of low-temperature poly-Si TFT``s. The oxide grown on poly-Si film had smooth interface with the poly-Si film, and exhibited better electrical characteristics than th...